High power LEDs are commonly used in luminaires for example in the architectural lighting industry—in stores, in offices and businesses; as well as in the entertainment industry—in theatres, television studios, concerts, theme parks, night clubs and other venues. In such applications LED arrays are frequently used to present images to an audience. It is common when projecting large images for the images to be divided into parts and then the parts transmitted to portions of the array. The transmission of these images can require significant bandwidth. In such applications the LED arrays are also frequently used to project a beam of light.
In these applications it is a common requirement to obtain the maximum light possible out of the LEDs without exceeding their operating temperature. LEDs are highly temperature sensitive and running them at too high a temperature will both reduce their output and shorten their life. In such applications, it is also frequently desirable to have the appearance of the image, light beam or plurality of light beams from a plurality of LED arrays be of consistent luminosity.
It is well known in the art to include a temperature sensor in an LED system to measure the temperature of the LEDs and use that information to control the operating current and voltage so that the LED always operates within safe operating parameters. However, the critical temperature is that of the LED semiconductor die itself and such temperature probes are often situated to measure the LED package or the heat sink rather than directly measuring the temperature of the die. To compensate for this many manufacturers include a safety band or dead space in the operating parameters to ensure that the temperature never rises too high. This safety band means that the LEDs are never achieving maximum possible brightness.
It is also known to consider the total power and heat dissipation of a bank of LEDs rather than that for each individual LED. If, for example, the luminaire has Red, Green and Blue LEDs mounted on a single circuit board or heat sink then if only the Red LEDs are illuminated it is possible to run those Red LEDs at a higher power than if all three groups, Red, Green and Blue were illuminated simultaneously.
These LED array fixtures are also used to project color light beams. For color control it is common to use an array of LEDs of different colors. For example a common configuration is to use a mix of Red, Green and Blue LEDs. This configuration allows the user to create the color they desire by mixing appropriate levels of the three colors. For example illuminating the Red and Green LEDs while leaving the Blue extinguished will result in an output that appears Yellow. Similarly Red and Blue will result in Magenta and Blue and Green will result in Cyan. By judicious control of the LED controls by color the user may achieve any color they desire within the color gamut defined by the LED colors employed in the array. More than three colors may also be used. For example it is well known to add an Amber or White LED to the Red, Green and Blue to enhance the color mixing and improve the gamut of colors available.
The differently colored LEDs may be arranged in an array in the luminaire where there is physical separation between each LED, and this separation, coupled with differences in die size and placement for each color, may affect the spread of the individual colors and results in objectionable spill light and color fringing of the combined mixed color output beam. It is common to use a lens or other optical device in front of each LED to control the beam shape and angle of the output beam; however these optical devices are commonly permanently attached to the luminaire requiring tools and skilled labor to change and may additionally need to be individually changed for each LED or pixel individually. It would be advantageous to be able to simply and rapidly change such optical devices for the entire array simultaneously without the use of tools.
There is a need for an inexpensive LED driving system which can maximize the output of connected LEDs in a luminaire while making the luminosity consistent across an array of LED array luminaires. There is also a need for a system and method that allows for the display of images or light patterns across an array of luminairs the display of which is controlled with conventional relatively low bandwidth control protocol.
There is also a need for a beam control system for an LED array luminaire which can be quickly and easily changed and provide improvements in spill light reduction and beam angle control.